Lithium secondary battery

Abstract: Provided is a lithium secondary battery excellent in initial charge/discharge characteristics and high in capacity comprising lithium-rechargeable cathode and anode and a nonaqueous electrolyte, wherein at least one of the cathode and the anode contains one of the following (A), (B) and (C): (A) a composite material comprising a carbon powder and a binder, which is treated with a silane coupling agent, (B) a composite material comprising a binder and a mixed carbon powder containing 70-99% by weight of a graphite powder and 30-1% by weight of a pseudo-graphitic carbon black, and (C) a composite material comprising a composite oxide powder of lithium and a transition metal, a conductive powder and a binder, which is treated with a silane coupling agent.

Description: The present invention relates to an electrode for a lithium secondary battery excellent in initial charge/discharge characteristics and cycleability and to a lithium secondary battery made using the electrode. A lithium secondary battery having, for example, a battery construction in which an electrode containing lithiated cobalt dioxide is used as a cathode and an electrode containing a carbon material is used as an anode utilizes the electrochemical reversible reaction in which lithium from the cathode is doped into the anode through an electrolyte at a charging stage, and the lithium is undoped from the anode and doped into the cathode through the electrolyte at a discharging stage. Characteristics required for the electrodes are a large doping ability (capacity) and undoping ability (capacity) and less deterioration in capacity at the doping and undoping cycle. From these viewpoints, various proposals have been made for electrodes containing carbon materials capable recharging of lithium and for batteries using such electrodes. Specifically, there have been proposed various batteries made using as the anode a wide variety of carbon materials including graphite materials or carbon materials having a random layer structure, such as batteries made using a graphite anode containing rechargeable lithium in the crystal (Japanese Patent Kokai (Unexamined Publn.) No. 57-208079), batteries made using an anode of a graphitic material comprising graphitizable spheroidal particles (Japanese Patent Kokai (Unexamined Publn.) No. 4-115457), batteries made using an anode of carbon material having a pseudo-graphite structure prepared by carbonizing organic polymer compounds (Japanese Patent Kokai (Unexamined Publn.) No. 62-122066), batteries made using an anode of carbon material having a specific structure (Japanese Patent Kokai (Unexamined Publn.) No. 62-90863), and batteries made using an anode of carbon material having a random layer structure (Japanese Patent Kokai (Unexamined Publn.) No. 2-66856). Furthermore, as for cathode materials, there have been proposed batteries made using as a cathode a metallic chalcogen compound or a carbon material having a specific structure prepared by carbonizing an organic polymer compound (Japanese Patent Kokai (Unexamined Publn.) No. 62-122066) and batteries made using as a cathode a composite oxide comprising an alkali metal and a transition metal and additionally Al, In or Sn (Japanese Patent Kokai (Unexamined Publn.) No. 62-90863). As a result of experiments and investigations conducted by the inventors using a wide variety of carbon powders for electrodes, it has been confirmed that among carbon powders, graphite powders are preferred as anode materials for lithium secondary batteries in view of the facts that they have a large doping and undoping ability for lithium and the voltage at which lithium is undoped is close to the lithium potential, but there is the problem that the initial charge/discharge characteristics are insufficient and batteries of a high capacity cannot be obtained. That is, in the case of the battery construction having an electrode containing a lithium-rechargeable material and an electrode containing a carbon powder, 100% of the lithium doped in the carbon material is not undoped in the initial stage and the utilizing efficiency of lithium is low and batteries of a high capacity cannot be obtained. In other words, a large amount of initial irreversible capacity components (irreversible capacity component = charging capacity of lithium to carbon material electrode - discharging capacity of lithium from carbon material electrode) are present in the carbon materials. Specifically, the capacity of an electrode containing a carbon material to dope and undope lithium per unit weight differs greatly depending upon the kind of the carbon material and is about 100-300 mAH/g. However, the irreversible capacity at the initial charging and discharging is also very high, namely, about 150-600 mAH/g for graphite materials and about 1000 mAH/g for carbon black and vapor-grown carbon materials made using iron catalysts. Therefore, batteries made using the electrodes containing these carbon materials are low in utilizing efficiency of lithium and batteries of a high capacity cannot be obtained. On the other hand, electrodes containing LiCoO 2 or LiNiO 2 which are a composite oxide of an alkali metal and a transition metal have an irreversible capacity of about 40 mAH/g at the initial charging and discharging and the utilization efficiency of lithium is insufficient. Furthermore, in making a sheet electrode, there are problems that bonding between the current collector and the electrode layer is insufficient and separation occurs therebetween and, as a result, fabrication of the sheet electrode is difficult, or in the case of a battery made using a sheet electrode insufficient in the bonding, the electrode layer comes off from the collector due to charging and discharging to cause degradation of the cycling behavior. An object of the present invention is to provide a lithium secondary battery of a high capacity which is excellent in initial charge/discharge characteristics by reducing irreversible capacity of electrodes at the initial charging and discharging stage and thus improving utilization efficiency of lithium. Another object is to provide a lithium secondary battery excellent in cycleability by improving the bond strength between the current collector and the electrode layer. As a result of conducting various investigations in an attempt to solve the above problems, the inventors have found that the irreversible capacity of an electrode containing a lithium-rechargeable material can be considerably reduced by treating the material with a silane coupling agent or by using a mixture of a graphite powder and a pseudo-graphitic carbon black as the material and that in making a sheet electrode the bond strength between the current collector and the mixed electrode layer can be considerably improved by treating the collector with a silane coupling agent. That is, the present invention is defined by the following features. (1) A lithium secondary battery comprising a lithium-rechargeable cathode and anode and a nonaqueous electrolyte, characterized in that at least one of the cathode and the anode contains one of the following (A) and (B): (A) a composite material comprising a carbon powder and a binder, which is treated with a silane coupling agent, (B) a composite material comprising a composite oxide powder of lithium and a transition metal, a conductive powder and a binder, which is treated with a silane coupling agent, with the proviso that the cathode does not contain an organic active material covalently bonded to the inorganic active material; Preferred embodiments are set out below (2) A lithium secondary battery described in the above (1), wherein the carbon powder of (A) contains a natural graphite powder or a artificial graphite powder as a sole component or a main component; (3) A lithium secondary battery comprising a lithium-rechargeable cathode, a lithium-rechargeable anode and a nonaqueous electrolyte, characterized in that the anode contains (A) described in the above (1); (4) A lithium secondary battery comprising a lithium-rechargeable cathode, a lithium-rechargeable anode and a nonaqueous electrolyte, characterized in that the cathode contains (B) described in the above (1); (5) A lithium secondary battery comprising a lithium-rechargeable cathode, a lithium-rechargeable an anode and a nonaqueous electrolyte, characterized in that the anode contains (A) described in the above (1) and the cathode contains (B) described in the above (1); and (6) A lithium secondary battery as characterized under (1) to (5) above wherein at least one of the electrodes is a sheet electrode obtained by forming a lithium-rechargeable electrode layer on a current collector, including a step of coating the surface of the current collector with a silane coupling agent and drying it before forming the electrode layer. First, the electrode containing the composite material (A) will be explained. The carbon powder used in the composite material (A) may be any of those which can dope and undope lithium by charging and discharging. Examples of the carbon powder are powders of natural graphite, artificial graphite, coke, carbon black, vapor-grown carbon, carbon fibers, materials obtained by carbonizing organic polymer compounds, materials obtained by heat-treating these materials and mixtures thereof. Especially, the carbon powder for anode is preferably one which undopes lithium at a voltage near the lithium potential and preferably comprises graphite as a sole component or as a main component. Furthermore, this graphite preferably has an interlayer spacing (d 002 ) of 3.37 Å or less in X-ray diffraction and a true density of 2.23 or more. The interlayer spacing (d 002 ) here means a value measured by an X-ray diffractometry using CuKα ray as X-ray and a high purity silicon as a standard substance [See Sugio Otani, "Carbon Fiber", P733-742 (1986) published from Kindai Henshu Sha]. The particle size of the carbon powder used in the present invention is not particularly limited, but usually is about 10 nm to 50 µm in number-average particle size. The binder used in the composite material (A) is for binding carbon particles together and is not limitative and may be any of those which have a binding effect and a resistance against the nonaqueous electrolyte used and against the potential at the cathode and anode. Examples of the binder are fluoropolymers, polyethylene and polypropylene. The amount of the binder is preferably about 0.1-20 parts by weight, more preferably 1-12 parts by weight for 100 parts by weight in total of the powders used. The silane coupling agent used in the composite material (A) includes the compounds represented by the following formula (1): YSiX 3 wherein Y is CH 2 =CH-, CH 2 =C(CH 3 )COOC 3 H 6 -, HN 2 C 3 H 6 -, NH 2 C 2 H 4 NHC 3 H 6 -, NH 2 COCHC 3 H 6 -, CH 3 COOC 2 H 4 NHC 2 H 4 NHC 3 H 6 -, NH 2 C 2 H 4 NHC 2 H 4 NHC 3 H 6 -, SHC 3 H 6 -, ClC 3 H 6 -, CH 3 -, C 2 H 5 -, C 2 H 5 OCONHC 3 H 6 -, OCNC 3 H 6 -, C 6 H 5 -, C 6 H 5 CH 2 NHC 3 H 6 -, C 3 H 5 NHC 3 H 6 -, or the like and X is -OCH 3 , -OC 2 H 5 , -OCOCH 3 , -OC 2 H 4 OCH 3 , -N(CH 3 ) 2 , -Cl or the like. As examples of the silane coupling agent, mention may be made of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltrichlorosilane, vinyltris(2-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, γ-ureidopropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, phenyltriethoxysilane and phenyltrimethoxysilane. Of these silane coupling agents, preferred are vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, γ-ureidopropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropyltriethoxysilane. More preferred are vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and γ-glycidoxypropyltrimethoxysilane. The mechanism in which the excellent effect can be obtained by the treatment with the silane coupling agent is not clear, but it can be considered that the surface adsorbed water or surface functional group which is considered to chemically react with lithium to prevent lithium from taking part in the charge/discharge reaction of the battery is reduced due to the improvement of water resistance (oleophilicity). Accordingly, titanate coupling agents or aluminate coupling agents which can be expected to have the similar effect are applicable. The amount of the silane coupling agent used in the present invention is not particularly limited, but is preferably determined taking into consideration the specific surface area of the carbon powder used. That is, since it is estimated that the silane coupling agent can cover the area of about 100-600 m 2 per 1 g [expressed by S (m 2 /g)] though it depends on the kind of the coupling agent, it is preferred that the amount of the silane coupling agent of A/S (g) per 1 g of the carbon powder is taken as one standard when the specific surface area of the carbon powder used is expressed by A (m 2 /g). However, even when the silane coupling agent is used in such an amount as being not able to cover the total surface area of the carbon powder, the irreversible capacity can be greatly reduced. In more detail, amount of the silane coupling agent is preferably 0.01-20 parts by weight, more preferably 0.1-10 parts by weight, most preferably 0.5-5 parts by weight for 100 parts by weight of the carbon powder used. Moreover, the method of treating the carbon powder and the binder of the composite material (A) with the silane coupling agent is not particularly limited, but as one example, mention may be made of a method which comprises reacting the silane coupling agent with water to hydrolyze a part or the whole of the silane coupling agent, mixing the hydrolysate in a desired amount with the carbon powder, drying the mixture and mixing the dried mixture with the binder. Furthermore, the treatment can also be performed by adding the silane coupling agent at the time of mixing of the carbon powder and the binder. Alternatively, the treatment can also be performed by previously adding the silane coupling agent to the binder or previously adding the silane coupling agent to a solution in which the binder is dissolved or dispersed and mixing therewith the carbon powder. The electrode containing the composite material (B) will be explained. As the transition metal in the composite oxide powder of lithium and the transition metal used in the composite material (B), mention may be made of, for example, Co, Ni, Mn, Fe, V, Mo and Ti. The conductive powder used in the composite material (B) is not limitative as far as it can impart electric conductivity when added in a suitable amount to the composite oxide powder of lithium and the transition metal. Examples are carbon powders such as graphite, acetylene black and carbon black and metal powders stable at the electrode potential used. The binder and the silane coupling agent used in the composite material (B) can be the same as used in the composite material (A). The method of treatment with the silane coupling agent is not limitative and as one example, mention may be made of a method which comprises reacting the silane coupling agent with water to hydrolyze a part or the whole of the silane coupling agent, mixing the hydrolysate in a given amount with a mixed carbon powder containing a composite oxide powder of lithium and the transition metal and a conductive powder, drying the mixture and mixing the dried mixture with a binder. Alternatively, the silane coupling agent is added at the time of mixing the composite oxide powder, the conductive powder and the binder or the silane coupling agent is previously added to the binder or to a solution or dispersion of the binder and the resulting mixture is mixed with the composite oxide powder and the conductive powder. In the lithium secondary battery of the present invention, at least one of the electrodes containing the composite material (A) or (B) is used. These electrodes can be used as either the cathode or the anode of the lithium secondary battery, but the electrode containing the composite material (A) is preferably used as the anode and the electrode containing the composite material (B) is preferably used as the cathode. The method for making the electrode for the lithium secondary batteries according to the present invention will be explained. The composite material (A) or (B) is uniformly mixed and press molded or is made into a paste using an organic solvent or the like and the paste is coated on a current collector and dried and then the coated collector is pressed. Especially, in the method of making a sheet electrode by forming on a current collector a lithium-rechargeable electrode layer, it is preferred to include a step of coating the silane coupling agent on the surface of the current collector and drying the coat before forming the electrode layer. The silane coupling agent used here can be the same as used in the composite material (A). As the current collector, there can be used a conductor which is electrochemically stable against the cathode material, the anode material and the nonaqueous electrolyte. Examples thereof are nickel, titanium, stainless steel, copper and aluminum. The method of coating the silane coupling agent on the surface of the current collector is not limited and one example is a method which comprises reacting the silane coupling agent with water to hydrolyze a part or the whole thereof, coating the resulting solution on the surface of the current collector and then drying the coat. The concentration of the solution of the silane coupling agent used here is preferably about 0.01-5% by weight, more preferably about 0.1-3% by weight. Furthermore, the surface of the current collector is preferably previously subjected to roughening treatment before coating of the silane coupling agent to further increase bonding effect. The degree of roughening is preferably about 0.1-10 µm and the roughening treatment includes, for example, mechanical polishing, electronic polishing and chemical polishing. In the lithium secondary battery of the present invention, it is preferred to use the electrode obtained by the method described above as at least one of electrodes. As the nonaqueous electrolyte used in the lithium secondary battery of the present invention, preferred is a solution of a lithium salt in an organic solvent of high dielectric constant. The lithium salt is not limited and there may be used, for example, LiClO 4 , LiPF 6 , LiBF 4 and LiCF 3 SO 3 . Concentration of the lithium salt is usually about 0.5-1.5 mol/l. The organic solvents can be those which dissolve the lithium salt to give electrical conductivity and are electrochemically stable against the anode material and the cathode material. The organic solvents include, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, acetonitrile, sulfolane and γ-butyrolactone. They are normally used as a mixed solvent of two or more. In the lithium secondary battery of the present invention, it is preferred to use the cathode, the anode and the nonaqueous electrolyte in combination with a separator which has functions to prevent the cathode and the anode from contacting with each other and to hold the nonaqueous electrolyte and is permeable to lithium ion. As the separator, mention may be made of microporous films such as polyethylene, polypropylene and polytetrafluoroethylene and nonwoven fabrics and woven fabrics. The thickness of the separator is preferably about 10-200 µm. The lithium secondary battery of the present invention can be in various forms such as cylindrical form, box form, coin form, button form, paper form and card form. The present invention will be illustrated by the following nonlimiting examples and comparative examples. Example 1 One part by weight of a silane coupling agent (A186 manufactured by Nippon Unicar Co., Ltd.) previously dispersed in pure water was added to 100 parts by weight of natural graphite (occurrence: Madagascar) powder heat-treated at 3000°C and having a number-average particle size of 10 µm, a specific surface area of 9 m 2 /g according to a nitrogen adsorption method, a true density of 2.26, an interlayer spacing d 002 of 3.36 Å in X-ray diffraction and an ash content of 0.05% by weight, followed by sufficiently mixing them. The mixture was vacuum-dried at 150°C to obtain a carbon powder treated with the silane coupling agent. Then, to 97 parts by weight of the product treated with the silane coupling agent was added, as a binder, 3 parts by weight of polyvinylidene fluoride dissolved in N-methylpyrrolidone as a solvent, followed by sufficiently kneading them. Thereafter, a part of the kneaded product was coated on a stainless steel mesh and pressed and dried to obtain an electrode containing 26.9 mg of the carbon powder. In order to evaluate the charge/discharge characteristics of the resulting electrode, a secondary battery for evaluation was fabricated by using a lithium foil as a counter electrode, a solution (1 mol/l in concentration) prepared by dissolving lithium perchlorate in a mixture of ethylene carbonate (EC) and 1,2-dimethoxyethane (DME) (in equal volume) as a nonaqueous electrolyte and a polypropylene separator of 175 µm thick which held the said electrolyte. The open-circuit voltage of the battery for evaluation before testing was 2.95 V. Then, the electrode containing the composite material comprising the carbon powder and the binder treated with the silane coupling agent was evaluated by doping lithium in the electrode (i.e., lithium charging) with a constant current of 0.5 mA until the voltage reached 0.00 V and thereafter, undoping lithium from the electrode (i.e., lithium discharging) with a constant-current of 0.5 mA until the voltage reached 1.5 V. The results are shown in Table 1. The charging capacity in Table 1 means the capacity of doping lithium in the electrode. Example 2 An electrode containing 27.4 mg of carbon powder was made in the same manner as in Example 1, except that A1160 manufactured by Nippon Unicar Co., Ltd. was used as the silane coupling agent, and the initial charge and discharge test with a lithium counter electrode was conducted. The results are shown in Table 1. Reference Example 3 75 parts by weight of the natural graphite used in Example 1, 25 parts by weight of pseudo-graphitic carbon black (TB3800 manufactured by Tokai Carbon Co., Ltd.) subjected to graphitization at 2800°C and having a true density of 2.04, an interlayer spacing d 002 of 3.40 Å in X-ray diffraction, a crystallite size (Lc) of 120 Å, a volatile content of 0.1% by weight, a number-average primary particle size of 66 nm and a specific surface area of 30 m 2 /g according to nitrogen adsorption method, and, as a binder, 5.4 parts by weight of polyvinylidene fluoride dissolved in N-methylpyrrolidone as a solvent were sufficiently uniformly kneaded, and a part of the kneaded product was coated on a stainless steel mesh and pressed and dried to obtain an electrode containing 48.7 mg of carbon powder. Reference Example 4 An electrode containing 49.9 mg of carbon powder was made in the same manner as in Reference Example 3, except that the natural graphite was used in an amount of 95 parts by weight, the pseudo-graphitic carbon black was used in an amount of 5 parts by weight and the polyvinylidene fluoride was used in an amount of 3.7 parts by weight. Example 5 To 91 parts by weight of lithiated nickel dioxide powder having a specific surface area of 1 m 2 /g measured according to nitrogen adsorption method and 6 parts by weight of acetylene black having a specific surface area of 60 m 2 /g as a conductive powder was added 20 parts by weight of a solution prepared by previously sufficiently mixing a silane coupling agent (A186 manufactured by Nippon Unicar Co., Ltd.) with pure water and ethanol at the silane coupling agent : pure water : ethanol=5:5:90 (part by weight). After sufficiently mixing them, the mixture was vacuum-dried at 150°C to obtain a mixture treated with the silane coupling agent. 97 parts by weight of the mixture was mixed with 3 parts by weight of polyvinylidene fluoride (a binder) dissolved in N-methylpyrrolidone as a solvent and the resulting mixture was coated on a stainless steel mesh and pressed and dried to obtain an electrode containing 43.8 mg of lithiated nickel dioxide. In order to evaluate the charge/discharge characteristics of the resulting electrode, a battery was fabricated in the same manner as in Example 1. The battery before the test had an open-circuit voltage of 3.11 V. Then, lithium was undoped from the electrode with a constant current of 0.5 mA until the voltage reached 4.20 V (i.e., battery charging) and thereafter, lithium was doped in the electrode with a constant current of 0.5 mA until the voltage reached 2.50 V (i.e., battery discharging). The results are shown in Table 1. Reference Example 6 An electrode (1) containing 25.8 mg of a mixed carbon powder of natural graphite and pseudo-graphitic carbon black was made in the same manner as in Reference Example 3. An electrode (2) containing 47.9 mg of lithiated nickel dioxide was made in the same manner as in Example 5 except that the mixed powder which was not treated with the silane coupling agent was used in place of the mixed powder of lithiated nickel dioxide powder and acetylene black which was treated with the silane coupling agent. In the same manner as in Example 1, a battery was fabricated using the electrode (1) and the electrode (2) and using the same electrolyte and separator as used in Example 1. The open-circuit voltage of this battery before testing was 0.12 V. Then, the battery in which the electrode (2) was used as a cathode and the electrode (1) was used as an anode was charged with a constant current of 0.5 mA until the voltage reached 4.15 V and then discharged with a constant current of 0.5 mA until the voltage reached 2.5 V. Example 7 An electrode (3) containing 26.3 mg of carbon powder treated with a silane coupling agent was made by using the mixed carbon powder of Reference Example 4 treated with the silane coupling agent in the same manner as in Example 1. Further, an electrode (4) containing 48.6 mg of lithiated nickel dioxide was made in the same manner as in Reference Example 6. In the same manner as in Reference Example 6, a battery was fabricated using these electrode and the charge and discharge test was conducted. The results are shown in Table 1. Comparative Example 1 A battery was fabricated in the same manner as in Example 1, except for using an electrode containing 27.4 mg of natural graphite powder which was not subjected to the treatment with the silane coupling agent and was vacuum-dried at 150°C in place of the natural graphite powder subjected to the treatment with silane coupling agent, and charge and discharge test was conducted. The results are shown in Table 1. Comparative Example 2 The charge and discharge test was conducted in the same manner as in Example 5, except that an electrode containing 52.1 mg of lithiated nickel dioxide which was not subjected to the treatment with the silane coupling agent was used in place of the electrode containing lithiated nickel dioxide subjected to the treatment with the silane coupling agent. The results are shown in Table 1. Comparative Example 3 An electrode (7) containing 26.5 mg of natural graphite was made in the same manner as in Comparative Example 1. Furthermore, an electrode (8) containing 48.7 mg of lithiated nickel dioxide was made in the same manner as in Reference Example 6. In the same manner as in Reference Example 6, a battery was fabricated using these electrodes, and the charge and discharge test was conducted. The results are shown in Table 1. According to the present invention, a lithium secondary battery which is reduced in irreversible capacity at the time of initial charging and discharging, improved in utilization efficiency of lithium and excellent in initial charge/discharge characteristics and cycleability can be provided.

Claims: A lithium secondary battery comprising a lithium-rechargeable cathode, a lithium-rechargeable anode and a nonaqueous liquid electrolyte, characterized in that at least one of the cathode and the anode contains one of the following (A) and (B): (A) a composite material comprising a carbon powder and a binder, which is treated with a silane coupling agent, (B) a composite material comprising a composite oxide powder of lithium and a transition metal, a conductive powder and a binder, which is treated with a silane coupling agent, with the proviso that the cathode does not contain an organic active material covalently bonded to the inorganic ative material. A lithium secondary battery according to claim 1, wherein the carbon powder of (A) contains a natural graphite powder or an artificial graphite powder as a sole component or a main component. A lithium secondary battery according to claim 1, wherein the anode contains the composite material (A). A lithium secondary battery according to claim 1, wherein the cathode contains the composite material (B). A lithium secondary battery according to claim 1, wherein the anode contains the composite material (A) and the cathode contains the composite material (B). A lithium secondary battery according to any of claims 1 to 5, wherein at least one of the cathode and the anode is a sheet electrode obtained by forming a lithium-rechargeable electrode layer on a current collector, including a step of coating a silane coupling agent on the surface of the current collector and drying the coat before forming the electrode layer.

Inventors: DEGUCHI TOSHIHISA, FURUKAWA YASUHITO, SATOH TOMOARI, TATENO TATSUO, DEGUCHI, TOSHIHISA, FURUKAWA, YASUHITO, SATOH, TOMOARI, TATENO, TATSUO
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY LIMITED
Application year: 1994
Main classification: H01M4
IPC codes: H01M4